Characterization of residual debris on packaged hip arthroplasty stems demonstrates the dominance of less than 10 μm sized particulate: Updated USP788 guidelines for orthopedic implants

Abstract

Past evaluation of particle contamination on packaged implants has typically been conducted using US Pharmacopeia (USP) 788, a 1970s pharmaceutical guideline created to evaluate contaminant particles in injectable fluids and syringes. Our objective was to reestablish relevant acceptance criteria for residual orthopedic and other implant debris, including smaller particles (i.e., <10 μm in diameter). Packaged total hip arthroplasty (THA) titanium (Ti6Al4V)-alloy femoral stems were used (hydroxyapatite [HA]-coated and non-coated stems). Short-term ultrasonication and longer-term 24-hour soak/agitation methods were used to elute surface-bound contaminant particles, and released particles were analyzed via scanning electron microscopy, energy-dispersive x-ray analysis, image analysis, and particle characterization. For HA-coated THA-stems, >99% of eluted particles were calcium phosphate. For plain non-coated THA-stems, >99% of eluted particles were titanium-alloy-based. The number-based median size of particles in both groups was approximately 1.5 μm in diameter despite being composed of different materials. The total volume of particulate removed from HA-coated stems was 0.037 mm³ (671 × 10³ particles total), which was approximately >50-fold more volume than that on plain non-coated stems at 0.0006 mm³ (89 × 10³ particles total). Only non-coated THA stems passed reestablished USP788 acceptance criteria, compared by using equivalent total volumes of contaminant particulate within new and legacy guideline ranges of >10 and >25 μm ECD, that is, <1.0 × 10⁷ particles for <1 μm diameter in size, <600,000 for <1–10 μm, <6000 for 10–25 μm and <600 for >25 μm. These results fill a knowledge gap on how much residual debris can be expected to exist on packaged implants and can be used as a basis for updating acceptance criteria (i.e., termed USP788-Implant [USP788-I]). Residual implant particulate assessment is critical given the increasing implant complexity and new manufacturing techniques (e.g., additive manufacturing).